Apparatus for pyrolyzing reactants



Sept. 29, 1953 A. L. GLAESER APFARATUS FOR PYROLYZING REACTANTS 2 Sheets-Sheet l Filed Oct. 26, 1949 FIGLI ALFR ED L.GLAESE R.

IN VEN TOR.

AGEN' P 9, 1953 A. L. GLAESER 2,653,859

APPARATUS FOR PYROLYZING REACTANTS Filed Oct. 26, 1949 2 Sheets-Sheet 2 ALFRED L. GLAESER.

INVENTOR.

p 0 i BY AGEN'II Patented Sept. 29, 1953 UNITED STATES PATENT OFFICE APPARATUS FOR PYROLYZING REACTANTS Alfred L. Glacser, Claymont, Del., assigno' to Hercules Powde- Company, Wilmington, Del., a corporation of Delaware Application October 26, 1949, Serial No. 123590 3 Claims. 1

This invention relates to the pyrolysis of organc compounds and, more particularly, to an improved method and apparatus for pyrolyzing reactants such as the lower aliphatic acids and lower aliphatic ketones in a tubular pyrolysis turnace.

It is well known that pyrolysis reactions involving the decomposition or crackng of Organic materials are endothermic and that the reactions are carried out in a heated tube or tubes which must be supplied with considerable heat energy from some outside source. It follows, since such reactions are endothermic, that the rate and emciency at which the cracking reaction proceeds are functions of the temperature which can be maintained in the reaction mixture, and that this temperature in turn is directly efl`ected by the rate at which the reaction tube can absorb heat from its surroundings.

In order to promote such reactions as emciently as possible, the reaction tubes usually take the form of elongated tubes or coils having a high ratio of surface to Volume. These tubes are housed in a furnace and heated by bringing combustion gases into intimate contact with the tubes containing the material to be oracked. It is obvious that the rate at which a reaction tube can absorb heat from the hot combustion gases will depend on the temperature of the gases, with a higher gas temperature promoting a more rapid input of heat to the tube.

Heretofore, pyrolysis installations for the pyrolysis of lower aliphatic acids and ketones have been limited to the use of a low B. t. u. content fuel such as producer gas which burns to produce a low temperature luminous flame, usually below about 1300 C. High B. t. u. content fuels such as butane or propane which burn to produce a high temperature, nonluminous flamewith ame temperatures in the order of 1600 C. or higher have never been successfully used to supply heat or such pyrolysis installations. This fuel limi- *tation has been dictated largely by the fact that excessively high flame temperatures severely re- 'duce the life of reaction tubes by overheating. II the tubes are continuously subjected to temperatures in excess of about 1100 C., they are .susceptible to premature failure.

In the commercial production of ketene, acetic acid vapors, for example, in the presence of a catalyst are passed through tnbular reaction coils of' heat-resistant alloy disposed in aiumaoe. The heat input necessary to street :tracking is supplied by bringing combustion gases into intima e tact wi h t e :@act on ,mi a contam the acetic acid vapors. Heretofore, commercial installations for producing ketene by the pyrolysis of acetic acid have utilized producer gas for supplying pyrolysis heat. Since producer gas inherently burns with a long, lazy, fully luminous type of flame, it has been necessary to design the pyrolysis furnaces to utilize this type of pyrolysis heat. The furnaces themselves have been constructed with a series of chambers separated one from the next by partial partitions or barfie walls. The combustion fuel is fired in a separate combustion chamber in the fumace and the combustion gases are led in a. zigzag path around the bame walls and through the urnace chambers housing the reaction coils. such an arrangement necessarily means that a marked temperature gradient exists within the reaction zone oi the furnace, for the gases are obviously hottest when they first contact the reaction coils and rapidly become cooler 'as they proceed through the furnace. Since the pyrolysis reaction is highly endothermic, it is apparent that the efliciency of the reaction becomes markedly lower with lower temperatures. In efiect, this means that the portion of the reaction coil in which cracking actually occurs is restricted to that portion which is in contact only with the hottest cases.

It is, therefore, an object of the invention to provide a method and apparatus for obtaining an improved distribution of heat to a pyrolysis reaction.

.Another object of th invention is to provide a method and apparatus for utilizing a high B. t. u. content fuel which burns with a fiame temperature in excess of about 1600 C. to supply heat for a pyrolysis reaction.

Another object of the invention is to provide an improved method and apparats for regulating the heat input to a pyrolysis reaction.

Other objects of the invention will appear hereinafter, the novel features and combinations being set forth in the appended claims.

Generally described, the method for obtaining an improved distribution of heat input to a pyrolysis reaction in accordance with this invention comprises generating primary hot combustion gases in a primary heating zone, passing the primary hot combustion gases into contact with a reaction tube, generating additional hot combustion gases in at least one other heating zone, passing the additiona hot combustion gas'es into contact with the reaction tube and into the priniary hot combustion gases, and passing reactants through the reaction tube. When a high B. t. u. content fuel such as butane or propane is employed to supply the heat input for the pyrolysis reaction, the method comprises generating a supply of primary hot combustion gases by burning high B. t. u. content fuel in a primary heating zone, regulating the temperature of the primary hot combustion gases in the primary heating zone, bringing the regulating gases into contact with the reaction tube, and supplying additional heat to the pyrolysois reaction by introducing fresh hot combustion gases into the primary combustion gases in the reaction zone. For certain high B. t. u. content uels, such as, for example, No. 6 fuel oil, it is desirable to regulate the temperatur of the fresh hot combustion gases introduced in the reaction zone.

The apparatus for practicing the method of this invention comprises a primary heat zone, a reaction zone in juxtaposition to the primary heat zone, a reaction tube disposed in the reaction zone, primary fuel burning means disposed in the primary heat zone, at least one additional heat zone space-d apart from the primary heat zone and in juxtaposition to the reaction zone, and additional fuel burning means disposed in the additional heat zone or zones. When a high B. t. u. content fuel is employed to supply the heat input for the pyrolysis reaction, the apparatus is provided with means disposed within the primary heat zone for introducing a cooling fluid such as steam into the primary hot combustion gases. The cooling fluid mixes with and Controls the temperature of the primary hot combustion gases in the primary heating zone prior to coni tact with the pyrolysis tube. The apparatus may be provided with means in conjunction with the additional fuel burning means disposed in additional heat zones for introducing cooling fluid into the additional hot combustion gases to regulate them.

A preferred embodiment of the invention has been chosen for purposes of illustration and description and is shown in the accompanying drawngs forming a part of the specification wher-ein reference symbols refer to like parts wherever they occur.

Figure 1 is a vertical sectional view taken along the longitudinal axis of a pyrolysis furnace constructed in accordance with this invention;

Figure 2 is a horizontal sectional view taken along section 2-2 of Figure 1;

Figure 3 is a horizontal sectional view taken along section 3-3 of Figure 1; and

Figure 4 is a horizontal sectional View taken along section 4-4 of Figura 1.

With reference to the drawings, a furnace ll constructed of refractory material is provided with a preheat chamber !2, a superheat chamber !3, and a cracking chamber l4. The cracking chamber !4 is substantially longer than the preheat and the superheat chambers. A tubular preheat coil |5 with an inlet 16 is disposed in the preheat chamber [2. A tubular superheat coil Il, connected to the preheat coil 15, is disposed in the superheat chamber l3 and a tubular cracking or pyrolysis coil !8, connected to the superheat coil ll, is disposed in the cracking chamber l4. The preheat coil |5 and the superheat coil l' are connected by a U-shaped conduit IQ. similarly, the superheat coil I'l and the cracking coil !3 are connected by a U-shaped conduit 21. As illustrated, the U-shaped conduits 19 and 2! wh ch connect the coils are disposed externally of the furnace, but the connections can be disposed internally of the furnace if so 4 desired. The cracking coil [8 is provided with an outlet 22. Thus, in combination, the coils IS, IT and !8, the connecting conduits s and Zi, and the inlet IS and the outlet 22 form an elongated reaction zone.

It will be noted that the preheat coil !5 and the superheat coil |1 occupy a substantial portion of the chambers l2 and [3, while the cracking coil [8 is disposed in the up per portion of the cracking chamber l4, leaving the lower portion of the chamber unoccupied for combustion and control purposes hereinafter described.

With reference to Figure 4, the preheat chamber l2 and the superheat chamber !3 are connected at the bottom thereof with a passageway 23 which extends through the furnace wall separating the two chambers. The passageway is further extended to substantially encompass a bottom refractory partition 24 in the preheat chamber l2 and a bottom refractory partition 25 in the superheat chamber 13. The refractory partitions 24 and 25 are provided with a plurality of ports 24' and 25', respectively, which permits communication between the chambers !2 and l3 and the passageway 23. With reference to Figure 2, the superheat chamber |3 and the cracking chamber 14 are connected at the top thereof with a passageway 26 which extends through the urnace wall separating the two chambers. The passageway is further extended to substantially encompass a top refractory partition 21 in the superheat chamber !3 and a top refractory partition 28 in the cracking chamber 14. The refractory partitions 21 and 28 are provided with a plurality -of ports 27' and 28', respectively, which permits communication between the chambers !3 and I 4 and the passageway 25.

With reference to the drawings, the chamber I 2 is provided with an exit conduit 29 provided with a regulating damper 3l. The exit conduit 29 leads to a suitable stack (not shown). The chamber l2 is also provided with a tubular member 32 concentrically disposed in the space encircled by the preheat coil 15. The tubular member 32 forms an extension of the exit conduit 23 to a point approximately fiush With the top of the preheat coil l5.

The superheat chamber 13 is provided with a cylindrical member 33 closed at the top and concentrically disposed in the space encircled by the superheat coil l'l. The member 33 extends from the bottom of the superheat chamber l3 to approximately the top of the coil. The tubular member 32 and the cylindrical member 33 function as space reducers for the gases entering chambers !2 and I 3, respectively.

The chamber [4 is provided at its base with a centrally located adjustable uel burner 34. A plurality of adjustable uel burners 35 is disposed vertically in the walls of the chamber |4 in the space below the coil !8. The burners 34 and 35 enerate a supply of primary hot combustion gases for furnishing heat input for the pyrolysis reaction. The combustion space in chamber !4 into which burners 34 and 35 extend is termed the primary heat zone. This primary heating zone or primary heat release zone is in juxtaposition with the pyrolysis zone containing the cracking co l !8.

A plurality of adjustable, cooling jets 36 is disposed vertlcally in the walls of the chamber |4 in alternating relationship with the burners 35. The burners 35 and cooling jets 35 are arranged vertically in two banks (Figure 4) and are adapted, respectively, to burn fuel and inject temperature with normal'throughput of material.

As indicated previously, the fuel may be a low B. t. u. content fuel such as producer gas or any other fuel which burns with a low temperature fiame, usually below 1300 C. In this case, no regulation or control of the temperature of the primary combustion gases in the primary heat zone is necessary before they contact the reaction vessel in the reaction zone.

Preferably the fuel is a high B. t. u. content fuel such as propane, butane, fuel oil or any other fuel which burns with a high temperature :lame on the order of 1600 C. or higher. In this case, the primary hot combustion gases must be regulated or controlled in temperature in the primary heat zone before they contact the cracking tube. This is accomplished by introducing sufficient cooling fluid such as steam into the primary hot combustion gases in the primary heat zone to reduce their temperature below about 1300 C. Any combination of cooling fluid jets may be employed to accomplish the desired regulation and control of the temperature of the primary combustion gases within the primary heat zone.

In the embodiment illustrated in Figure 1 and Figure 4, burners and cooling fluid jets are disposed alternately in two vertical banks in the chamber walls to respectively fire and inject cooling fluid tangentially in the same rotational direction into the primary heat zone. This arrangement is quite advantageous, as it insures eficient mixing of the cooling uid with the primary hot combustion gases in the primary heat zone.

The preferred cooling fluid in accordance with the invention is steam. However, other cooling fiuids are satisfactory, such as nitrogen, carbon dioxide, or other inert gaseous materials. Water in liquid form is also suitable. Suicient cooling fluid is used to bring the temperature of the primary hot combustion gases to a value not in excess of about 1300 C. and to regulate and control the temperature of the primary hot combustion gases substantially at this level within the primary heat zone.

In accordance with the invention, at least one annular gas-fired ring is provided to supply additional and controlled heat input to the pyrolysis reaction. In the enbodiment illustrated in Figure 1, the ring is disposed concentrically in the chamber walls at a point approximately midway between the two ends of the cracking coil. However, this annular gas-fired ring can be suitably disposed at other points within or in juxtaposition to the reaction zone of the furnace. Also, additional similar annular gas-fired rings may be disposed at suitable points within or in juxtaposition to the reaction zone. It is contemplated within the scope of this invention that the heat required for the reaction may be supplied entirely by a plurality of suitably disposed annular gas-fired rings. The annular gas-fired rings are preferably constructed of silicon carbide brick which has a high rate of heat conductivity and therefore exposes a high temperature radiating surface for heat input to the spirals of the coil in juxtaposition thereto.

In the embodiment illustrated in Figure 2, a plurality of burners is disposed to fire into the passageway connecting the craclcing chamber with the superheat chamber. Instead of this arrangement, the burners may be positioned to fire into the passageway connecting the superheat chamber with the preheat chamber, or alternatlvely, burners may be positioned to fire into both of the passageways.

Any desired combination of burners in the annular gas-fired ring or rings and burners fired into the passageways can be employed, the only requirement being sufficient burner Capacity to maintain and control an even distribution of heat input to the pyrolysis reaction over a substantial proportion of the reaction zone.

For certain types of high B. t. u. content fuel such as, for example, No. 6 fuel oil, it is desirable to provide cooling fluid means disposed in conjunction with each means for generating hot combustion gases within the system in order to properly regulate these gases and insure an even distribution of heat input to the pyrolysis reaction over a substantial proportion of the reaction zone.

The following examples set forth three ways in which the principle of the invention has been practiced. It is to be understood, however, that the examples are purely' illustrative and are not to be construed as a limitation of the invention.

In the examples, ketene is produced by the pyrolysis of acetic acid in accordance with the apparatus depicted in the drawings wherein each of the burners 34, 35, 39 and M has a nominal or rated capacity of 2,700,000 B. t. u., 500,()00 B. t. u., 200,000 B. t. u., and 200,000 B. t. u. per hour, respectively, using propane as the fuel. The ketene formed is then reacted with glacial acetic acid in additional apparatus associated with the pyrolysis furnace to produce acetic anhydride.

Example I Four of the burners 35 were fired with propanc gas as fuel to generate a supply of primary hot combustion gases. Steam was introduced through the lowest disposed cooling fluid jet 36 to control and regulate the temperature of the hot combustion gases in the primary heat zone. The regulated gases were brought into contact with the cracking coil 18 and were supplemented by combustion gases generated by the two burners 39 firing into the annular gas-fired ring 3'! using propane throughout as fuel. The combustion gases were further supplemented by combustion gases generated by the two burners i, using propane as uel, firing into the passageway 25 which connects the cracking chamber M with the superheat chamber I3. Acetic acid vapors containing Catalyst were passed into the inlet IE at the rate of 1000 lb./hr. The burners and sto-am jet were adjusted so that the temperature of the gases throughout the cracking chamber and the superheat chamber was maintained between about 850 C. and about 1020 C. and remained so throughout the run, and at a level to promote the pyrolysis reaction at its maximum eiciency. This close temperature control over a substantial proportion of the reaction zone was made possible by regulating the temperature of the primary gases in the primary heat zone and by augmenting the regulated primary combustion gases with additional fresh combustion gases generated in the annular gas-fired ring and in the passageway connecting chambe's !3 and M. This control was not possible in the absence of the tempering steam and the augmenting additional fresh combustion gases. The total p'opane consumpticn was approximately 200 lb./hr. Approximately 3000 lb. of air/hr. was introduced at the burners to burn the propane, and approximately 750 lb. steam/hr. was introduced to regulate the temperature of the primary hot combustion gases. The ketene formed wasreated with glacial acetic acid in 'additional apparatus associated with the pyrolysis' furnace to produce acetic anhydride. A yield of 1 lb. of acetic anhydride for each 1.22 lb. of acetic acid passed through the pyrolysis furnace was obtained whereas the theoretic yield is 1,1bj. of acetic anhydride ior each 1.'1'78 lb. of acetic acid, !thus demonstrating a' satisfactory yield of ketene at 'a high rate of efliciency' i Example II The burner 34' was fired" with propane gas as fuel to generate a' supply' o'f primary hot combustion gases. steam was introduced through the lowest disposed cooling fluid jet 36 to control and regulate the temperature of the hot combustion gases in the primary heat zone. The regulated gases were supplemented in the cracking chamber by combustion gases generated by the two burners 39 firing into the annular gasfired ring 31, using propane as fuel. The combustion gases were further supplemented by combustion gases generated by the two burners 41, using propane as fuel. These burners fired into the passageway 26 which connects the cracking ehamber M with the superheat chamber !3. Acetic acid Vapors containing catalyst were passed into the inlet I'B at the rate of 1000 lb./hr. The burners and steam jet were adjusted so that the temperature of the gases throughout the cracking chamber and the superheat chamber was maintained between about 850 C. and about 1020 C. and remained so throughout the pyrolysis run, and at a level to promote the pyrolysis reacton at its optimum efficiency. Fuel, air and steam Consumption were substantially the same as in Example I, and substantially the same yield of ketene was obtained at substantially the same high rate of efliciency.

Example III This example was conducted under substantially the same conditions as Example II, but the throughput of acetic acid was increased to 1250 lb./hr. An increased yield of ketene was obtained without loss of efficiency.

The foregoing examples demonstrate the principle of the invention when acetic acid is pyrolyzed to produce ketene. The invention is by no means limited in its application. however. to the pyrolysis of acetic acid. It is equally applicable for the pyrolysis of other organic compounds, including acetone, methyl ethyl ketene. diethyl ketone, propionic acid, and butyric acid.

In the foregoing examples, it is demonstrated that a high B. t. u. content fuel such as propane can be employed satisfactorily as a source of heat input for a pyrolysis reaction. The temperature of the primary hot combustion gases was satisactorily controlled and regulated in the primary heat zone by the use of steam as a regulating agent. An improved distribution of heat input to the pyrolysis reaction is demonstrated in the examples by the fact that the temperature of the gases throughout the cracking and superheat zones was substantially the same. The advantages of the apparatus and method of the present invention are several. A high B. t. u. content fuel can be employed as the source of heat input for the pyrolysis reaction. thereby eliminating the investment cost of constructing and maintaining, and the cost of Operating a producer gas plant. The temperature of the combustion gases employed to supply heat to the pyrolysisraction controlled and regulated .over isub'stantial portion of .the reaction zone, and a' greatly improved distribution .ofheat inpit to the .pyro1ysis reaction is obtained.

What I claim and desire to protect by Letters Patentis p p W 1; In a pyrolysis furnace, the improvement which comprises a primary heat zone', a pyrolysis zone spaced from the primary heat zone and in direct communication therewith, a. pyrolysis coil disposed in the pyrolysis zone, primary fuel burning means and cooling jets disposed 'in the primary heat zone, a secondary heat zone spaced &part from the primary heat zone and in juxtaposition to the pyrolysis zone, said s'econdary heat zone being concentrically disposed around a portion of the pyrolysis coil intermediate the ends thereof, secondary fuel burning means disposed in the secondary heat zone, said secondary iuel burning means being an annular gas-fired ring for generation of name gases without impingement of said fiame gases on the pyrolysis coil and for passage of combustion gases from said annular gas-fired ring into direct contact with said pyrolysis coil, a superheat zone in spaced relationship to the pyrolysis zone, a. superheat coil disposed in the superheat zone, a chamber connecting the superheat zone with the pyrolysis zone, tertiary fuel burning means disposed in the chamber, a preheat zone in spaced relationship to the superheat zone, a preheat coil disposed in the preheat zone, a chamber connecting the preheat zone with the superheat zone, a space reducer disposed withn the superheat coil and a, space reducer disposed within the preneat co,sad latter spaced reducer acapted to permt passage of the combustion gases tnerethrough and Irom the i'urnace.

2. In a, pyrolysis furna-ce, the improvement which comprises a primary heat zone, a pyrolysis zone spaced from the primary heat zone and in direct communication therewith, a, pyrolysis tube disposed in the pyrolysis zone, primary fuel- 'burning means and steam jets disposed in the primary heat zone, a secondary heat zone spaced apart from the primary heat zone and in juxtaposition to the pyrolysis zone and being concentrically disposed around a portion of the pyrolysis tube intermediate the ends thereof, and secondary fuel-burning means disposed in the secondary heat zone comprising an annular gas-fired ring with burners disposed therein to produce fiame gases within said ring and to prevent impingement of flame gases on the pyrolysis tuoe, and with ports for passage of combustion gases from said ring into airect contact with the pyrolysis tube.

3. In a pyrolysis furnace, the improvement which comprises a primary heat zone, a pyrolysis zone spaced from the primary heat zone and in direct communication therewith, a, pyrolysis coil disposed in the pyrolysis zone, primary fuelburning means and steam jets disposed in the primary heat zone, a seconuary heat zone s aced apart irom the primary heat zone and in juxtaposition to the pyroysls zone and being concentrically disposed around a portion of the pyrolysis coil intermediate the ends thereof, secondary mel-burning means disposed in the secondary heat zone comprising an annular gasfired ring with burners disposed theren to produce fiame gases within said ring and to prevent impingement of fiame gases on the pyrolysis coil and with ports for passage of combustion gases from said ring into direct contact with the pyrolysis coil, a superheat zone in spaced. relatonsnp 11 to the pyrolysis zone, a superheat coil disposed in the superheat zone, a. chamber connecting the superheat zone with the pyrolysis zone, tertiary mel-burning means disposed in the chamber, a, preheat zone in spaced relatonship to the superheat zone, a. preheat col dsposed in the preheat zone, and a chamber connecting the preheat zone with the superheat zone.

ALFRED L. GLAESER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,378,307 Young May 17, 1921 1,61'7,297 Bell Feb. 8, 1927 Number 

1. IN A PYROLYSIS FURNACE, THE IMPROVEMENT WHICH COMPRISES A PRIMARY HEAT ZONE, A PYROLYSIS ZONE SPACED FROM THE PRIMARY HEAT ZONE AND IN DIRECT COMMUNICATION THEREWITH, A PYROLYSIS COIL DISPOSED IN THE PYROLYSIS ZONE, PRIMARY FUEL BURNING MEANS AND COOLING JETS DISPOSED IN THE PRIMARY HEAT ZONE, A SECONDARY HEAT ZONE SPACED APART FROM THE PRIMARY HEAT ZONE AND IN JUXTAPOSITION TO THE PYROLYSIS ZONE, SAID SECONDARY HEAT ZONE BEING CONCENTRICALLY DISPOSED AROUND A PORTION OF THE PYROLYSIS COIL INTERMEDIATE THE ENDS THEREOF, SECONDARY FUEL BURNING MEANS DISPOSED IN THE SECONDARY HEAT ZONE, SAID SECONDARY FUEL BURNING MEANS BEING AN ANNULAR GAS-FIRED RING FOR GENERATION OF FLAME GASES WITHOUT IMPINGEMENT OF SAID FLAME GASES ON THE PYROLYSIS COIL AND FOR PASSAGE OF COMBUSTION GASES FROM SAID ANNULAR GAS-FIRED RING INTO DIRECT CONTACT WITH SAID PYROLYSIS COIL, A SUPERHEAT ZONE IN SPACED RELATIONSHIP TO THE PYROLYSIS ZONE, A SUPERHEAT COIL DISPOSED IN THE SUPERHEAT ZONE, A CHAMBER CONNECTING THE SUPERHEAT ZONE WITH THE PYROLYSIS ZONE, TERTIARY FUEL BURNING MEANS DISPOSED, IN THE CHAMBER, A PREHEAT ZONE IN SPACED RELATIONSHIP TO THE SUPERHEAT ZONE, A PREHEAT COIL DISPOSED IN THE PREHEAT ZONE, A CHAMBER CONNECTING THE PREHEAT ZONE WITH THE SUPERHEAT ZONE, A SPACE REDUCER DISPOSED WITHIN THE PREHEAT COIL, SAID SPACE REDUCER DISPOSED WITHIN THE PREHEAT COIL, SAID LATTER SPACED REDUCER ADAPTED TO PERMIT PASSAGE OF THE COMBUSTION GASES THERETHROUGH AND FROM THE FURNACE. 